1. Field of the Invention
The present invention is directed to new and known substituted thiadiazole ureas. More specifically, the instant invention is directed to substituted thiadiazole ureas compositions useful as defoliants.
2. Description of the Prior Art
Certain substituted thiadiazole ureas are known in the art. For example, thiadiazole ureas having benzylthio substituents, substituents carrying halo, trifluoromethyl and other groups have been disclosed to be herbicidally active in U.S. Pat. Nos. 4,066,436; 4,141,717; and 4,217,459, all issued to Kirkpatrick. None of these patents disclose, suggest or make obvious the use of these compounds for defoliating plants.
U.S. Pat. No. 4,175,081, issued to Driscoll, discloses the use of other substituted thiadiazole ureas, such substitutions being among others p-chlorobenzylthio groups. Driscoll discloses the herbicidal use of these compounds. This reference, however, does not disclose, suggest or mention any defoliating efficacy, and certainly not any cotton defoliating efficacy, for any of the compounds disclosed in his patent.
As those skilled in the art are aware, herbicidal use of a compound involves the phytotoxic effect of that compound on plants. A compound possessing phytotoxic properties causes plant tissue death, including the destruction of stems and leaves. However, the leaves of the plant subject to such phytotoxicity usually remain attached to the main body of the plants. Eventually, the plant collapses and falls to the ground.
On the other hand, as those skilled in the art are also aware, a defoliant is selective in its destructive effect on a plant. A defoliant affects only the leaves of the plant, causing them to mature, while the main body of the plant, i.e., the stems, roots, and fruiting bodies remain essentially undisturbed. In many instances, regrowth of new leaves begins some time after application of the defoliant.
It is most important, however, that the use of a chemical defoliant be specific. That is, the effect of the defoliant should be limited to the elimination of leaves from the plant. In many instances, defoliants act in a manner similar to that of a herbicide. In those cases not only are the leaves eliminated from the plant, but, undesirably, the plant itself collapses prior to harvesting.
The importance of defoliation in the harvesting of certain crops cannot be overemphasized. Probably the best example of a crop where defoliation is critical to the success of a harvest is cotton. Even under the most optimum conditions cotton plants do not mature uniformly or soon enough to facilitate mechanical harvesting. That is, cotton bolls do not appear before the growth of leaves on the cotton plants. Unlike other crops which may be easily mechanically harvested, the leaves of the cotton plants interfere with mechanical harvesting of lint from cotton bolls. When the cotton plant is leafy, mechanical pickers cannot be efficiently utilized. This is because the leaves interfere with the actual picking process. Furthermore, the leaves cause excess trash accumulations. In addition, the green leaves stain the cotton fiber.
Cotton defoliation eliminates the leaves which thus eliminate the interference in the picking process, elimination of excess trash as well as the prevention of fiber staining. Moreover, a defoliated plant permits the cotton bolls to mature, allowing a "once through the field" type of harvest. Those skilled in the art are aware this type of cotton harvesting is most efficient.